It is known in packaging machines to manufacture the packages of a lower and an upper foil, recesses being formed in the lower and/or the upper foil. The goods is then placed into the recesses of the lower foil and is sealed by means of the upper foil to create a finished package. Following this sealing operation, the packages are then separated from one another, which is done by means of a longitudinal and a transverse cutting device. The two tool parts must carry out a relatively large stroke during the transverse cutting of the packages, so that the tool parts can engage between the cuplike formed lower foil and the possibly also cuplike formed upper foil. If the upper foil is not profiled, then the upper tool part is fixedly connected to the machine frame and only the lower tool part is lifted and lowered. If the upper foil is profiled, then the upper part must also be lifted and lowered. The upper part is, in the cutting position, fixedly locked to the machine frame. It is known to use a pneumatic drive for driving the cutting device, whereby the pneumatic drive acts onto a toggle-lever arrangement, which presses the lower part against the upper part fixed on the machine frame. The toggle-lever arrangement is needed in order to be able to apply forces, which can be 9 t. and higher. The disadvantages of the toggle-lever arrangement consists in same being exposed to a relatively high wear, and the opening width of the machine parts being limited, since insufficient space exists below the foil for the arrangement of the complicated mechanism. Moreover, this construction is also complicated and susceptible to wear, since it consists of many individual parts.
Furthermore it is known to provide a hydraulic drive, with which the high cutting forces can be produced substantially easier. However, this hydraulic drive is particularly problematic because when it is used during packaging of foods or of pharmaceutical goods, doubts exist regarding a possible leakage of hydraulic oil. Moreover, the hydraulic aggregate is also complicated and expensive to manufacture and an additional energy medium is needed, which does not exist like pressurized air exists at any rate.
The basic purpose of the invention is to provide a drive for punching, cutting and stamping devices of the above-mentioned type so that they can be manufactured with an opening gap of any size, that they can be operated at a low pressure when moving the tool parts together, so that additional safety devices are not needed, that the drive being relatively small in construction is simple in design and economical to manufacture and that the drive can produce at the same time the respectively needed closing force and thus the cutting, stamping and punching force.
According to the invention, the pneumatic drive for punching, cutting and stamping devices thus consists of at least one pneumatic cylinder, which is connected to a movable tool part. The piston rod of the pneumatic cylinder is connected to a further piston rod of a second air pressure clamping element which is fixed on the machine frame. If a flat upper foil is used here, it can at all times be fixedly connected to the machine frame. Otherwise, it must also be constructed liftably and lowerably.
The compressed-air cylinder, which is connected to the movable tool part, can be constructed with the necessary length, so that the tool part takes up the needed opening gap for the further transport of the packages. The compressed-air cylinder can be loaded with a relatively low pressure, so that the force exerted by it lies below 15 kp., namely below a force at which no injuries are to be feared and thus additional safety devices are not needed. The piston rod is mechanically blocked at the end of the closing movement by means of the pneumatic cylinder, whereby the blocking device can be integrated inside of the pneumatic cylinder or, however, by means of a bolt, which is inserted into a recess of the piston rod and thus fixes it relative to the cylinder. The lower tool part rests in this closed position of the lower tool part with a contact pressure of less than 15 kp. on the knife. Subsequently, compressed air is applied to the pressure clamping element, so that the now locked piston rod s loaded with a large force, which may be 9 t. or more, and the knife is in this manner pressed against the abutment, so that the foil is separated. The pressure clamping element consists of several piston cylinder units which are connected in series, so that the diameter of the pressure clamping element is held relatively low during a high production of force. The path, which the pressure clamping element must cover, may then only be a few mm., which is for example by all means sufficient for cutting of a foil. The path, however, can also be increased at the expense of the structural height in order to be sufficient for example for stamping and punching devices.
The pressure clamping element consists preferably of several individual parts held pressed against one another annularly. The individual parts have a center bore, through which the piston rod extends. A cylindrically shaped shoulder arranged on the piston extends also through the center bore, whereby each piston is supported on the preceding and the next following piston, so that at a relatively small diameter with several pistons arranged one behind the other, a high pressure can be built up. The compressed air is supplied and discharged in the annular parts through bores which extend through the parts and lie one above the other after installation. Thus, it is possible to supply the plurality of piston units, which lie one behind the other, with two outside pneumatic connections.
Two drive units are preferably used for a cutting tool which is used for packaging machines. The drive units are arranged on both sides of the cutting device, and the two pressure clamping elements are connected through plates on which is secured the tool part carrying the knife.
Thus, an inventive device makes it possible to create opening gaps of any size between the two tool parts, which are limited only by the height of the machine frame. The inventive device consists of comparatively few individual parts, which can be manufactured inexpensively and thus results in a very economical construction, which operates wear-free but still delivers the necessary great contact pressure Since, moreover, a moving together of the two tool parts occur with a relatively low pressure, not only a safety device is not needed, but also the air consumption as such is significantly reduced. The actual working stroke which is driven with a high air pressure, is thus limited to a minimum, so that the device as a whole operates very economically.